1. Field of the Invention
This invention relates to a semiconductor device, in particular, a semiconductor device having a capacitor.
2. Description of the Related Art
In recent years, ferroelectric memories (FeRAM: Ferroelectric Random Access Memory) using a ferroelectric film as dielectric film of a capacitor have been being developed.
In manufacturing ferroelectric memories, it is necessary to form various plugs connected to capacitors and transistors, etc. Aluminum (Al) is widely used as material of these plugs. However, with microminiaturization of elements, it is getting more difficult to fill contact holes with aluminum plugs. In particular, if a plug is formed in a deep contact hole, it is getting more difficult to apply aluminum.
Therefore, it is one choice to use tungsten (W) plugs having an excellent filling property, instead of aluminum plugs. However, tungsten tends to be oxidized, and thus a problem can occur that tungsten plugs deteriorate by annealing in oxygen atmosphere for improving the capacitor property. This can cause a problem of deterioration of property and reliability of ferroelectric memories due to contact failure or the like.
As prior art, Jpn. Pat. Appln. KOKAI Pub. No. 11-126881, Jpn. Pat. Appln. KOKAI Pub. No. 2001-44376, and U.S. Pat. No. 6,004,839 disclose a semiconductor device having a ferroelectric capacitor. However, the techniques disclosed in these documents relate to a protector for capacitor, such as a hydrogen barrier film, and protection of plugs is not considered at all.
As described above, conventional ferroelectric memories have the problem that filling contact holes with plug material is difficult with microminiaturization of elements, and the problem of deterioration of plug material due to oxidation. Therefore, it is difficult to obtain a semiconductor device having excellent property and reliability.